Why are certain premises at increased risk of equine grass sickness? A matched case-control study.
Authors: McCarthy H E, French N P, Edwards G B, Miller K, Proudman C J
Journal: Equine veterinary journal
Summary
# Editorial Summary: Grass Sickness Risk Factors on Individual Premises Equine grass sickness (EGS) demonstrates a troubling tendency to recur on certain properties, yet the underlying premises-level determinants remained poorly understood until this matched case-control investigation. McCarthy and colleagues compared 60 farms with confirmed EGS cases against 120 time-matched control premises, collecting detailed information on pasture management, soil and herbage nutrient composition, and meteorological data from the two weeks preceding disease onset. Conditional logistic regression analysis revealed three significant risk factors: elevated soil nitrogen content, evidence of pasture disturbance, and a history of EGS occurrence on the same property—notably, neither recent fertilisation practices nor harrowing regimes showed protective effects, and weather conditions proved non-significant in the study period. These findings suggest that soil chemistry and physical pasture disruption may enhance conditions favouring *Clostridium botulinum* spore germination or toxin production, warranting a fundamental reassessment of pasture management strategies on affected premises rather than relying on conventional fertilisation and maintenance routines. For practitioners advising on EGS-affected farms, this evidence points toward investigating soil nitrogen status and considering remedial strategies focused on pasture stabilisation, potentially offering more targeted prevention than standard husbandry modifications.
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Practical Takeaways
- •Premises with history of EGS require targeted prevention strategies; recurrence is not random but linked to environmental factors that persist on the farm
- •Soil nitrogen management and minimising pasture disturbance may help reduce EGS risk, though further research is needed to establish causation and optimal intervention strategies
- •Weather conditions alone do not explain EGS occurrence on high-risk premises; focus prevention efforts on modifiable soil and pasture factors rather than meteorological predictions
Key Findings
- •Increased soil nitrogen content was significantly associated with EGS occurrence on affected premises
- •Pasture disturbance was identified as a multivariable risk factor for EGS
- •Previous occurrence of EGS on premises was strongly associated with recurrent cases
- •Meteorological variables and common management practices (harrowing, fertilisation, reseeding) showed no significant association with EGS risk